DELAWARE, Ohio — Mocking his critics, Donald Trump pledged Thursday to fully accept the outcome of next month's presidential election — if he wins. The Republican said he reserved the right to contest questionable results, deepening his unsubstantiated assertions that the race against Hillary Clinton could be rigged against him.

Trump's comments came a day after his stunning refusal in the final presidential debate to say whether he would concede to Clinton if he loses. His resistance, threatening to undermine the essence of American democracy, was roundly rejected by fellow Republicans.

Arizona Sen. John McCain, the 2008 GOP nominee, called the peaceful transfer of power "the pride of our country."

"I didn't like the outcome of the 2008 election. But I had a duty to concede, and I did so without reluctance," McCain said in a lengthy statement. "A concession isn't just an exercise in graciousness. It is an act of respect for the will of the American people, a respect that is every American leader's first responsibility."

With the presidential race slipping away from him, Trump has repeatedly raised the specter of a rigged election, despite no evidence of widespread voter fraud heading toward Election Day or in previous presidential contests. His top advisers and running mate Mike Pence have tried to soften his comments, only to watch helplessly as he plunges ahead.

Asked in Wednesday's debate if he would accept the election results and concede to Clinton if he loses, Trump said: "I will tell you at the time. I will keep you in suspense."

"That undermines our democracy," President Barack Obama said while campaigning for Clinton in Florida. "Our democracy depends on people knowing their vote matters."

His wife, first lady Michelle Obama, told 7,000 Clinton supporters in Republican-voting Arizona Thursday that Trump was threatening to "ignore our voices and reject the outcome of this election." She said that's the same as "threatening the very idea of America itself."

Trump's comments overshadowed his attempts to diminish Clinton's credibility during the debate. He entered the contest desperate to reshape the race and attract new voters who are deeply skeptical of his brash temperament and fitness for office, but it appeared unlikely he accomplished those goals.

Campaigning Thursday in must-win Ohio, Trump tried to make light of the situation.

"I would like to promise and pledge to all of my voters and supporters and to all of the people of the United States that I will totally accept the results of this great and historic presidential election," he said. After letting that vow hang in the air for a few seconds, he added, "If I win."

The Republican nominee said he would accept "a clear election result" but reserved his right to "contest or file a legal challenge" if he loses. He brushed off the likelihood of that happening with a confident prediction that "we're not going to lose."

Yet numerous Republican leaders concede Trump is heading for defeat barring a significant shift in the campaign's closing days. The GOP's top concern now is salvaging its majority in the Senate, followed closely by worries over the Republicans' once comfortable grip on the House.

"The landscape has gotten a lot tougher for Republicans in the House," said Liesl Hickey, a Republican strategist involved some of those races. In Pennsylvania, Sen. Pat Toomey said Trump's comments were "irresponsible."

U.S. elections are run by local elected officials — Republicans, in many of the most competitive states.

Trump's campaign pointed to Al Gore and George W. Bush in 2000 as an example of why it would be premature for Trump to say he'd acquiesce on Nov. 8. That election, which played out for weeks until the Supreme Court weighed in, didn't center on allegations of fraud, but on proper vote-counting after an extremely close outcome in Florida led to a mandatory recount.

Trump tried to turn the tables on Clinton by accusing her of "cheating" and suggesting she should "resign from the race." He cited a hacked email that showed her campaign was tipped off about a question she'd be asked in a CNN town hall meeting during the Democratic primary.

"Can you imagine if I got the questions? They would call for the re-establishment of the electric chair, do you agree?" Trump said at a rally in Ohio.

Trump's effort to shift the conversation back to Clinton focused on an email from longtime Democratic operative Donna Brazile to Clinton's campaign in March with the subject line "From time to time I get the questions in advance." It contained the wording of a death penalty question that Brazile suggested Clinton would be asked.

Brazile, now the acting Democratic National Committee chairwoman, was a CNN contributor at the time she sent the email, one of thousands disclosed publicly by WikiLeaks after Clinton's campaign chairman's emails were hacked. Clinton's campaign has said Russia was behind the hack.

The rivals toned down the vitriol a little Thursday night at the Alfred E. Smith Memorial Foundation Dinner in New York, a white-tie gala in which politicians are expected to be light-hearted and funny. Still, Trump drew some jeers for calling Clinton "corrupt," while Clinton got personal with jokes about Trump's treatment of women and connections to Russia.